1. Field of the Invention
The present invention relates to a thermal transfer image receiving material which is used together with a thermal transfer recording material to form images thereon. In addition, the present invention relates to a thermal transfer recording method using the receiving material.
2. Discussion of the Related Art
In thermal transfer recording, imagewise heat is applied to a thermal transfer recording material, such as thermofusible thermal transfer recording materials and sublimation thermal transfer recording materials, whose ink layer contacts a thermal transfer image receiving material, to form an image on the receiving material. The receiving material is broadly classified into film receiving materials having a film substrate and paper receiving materials having a paper substrate. Film receiving materials have a smooth surface. However, when imagewise heat is applied to a thermal transfer recording material contacting a film receiving material to form images on the receiving material, the heat tends to diffuse through the receiving material, resulting in formation of poor images. Namely, the film receiving materials have poor thermosensitivity. In addition, films generally have poor cushion ability (hereinafter referred to as cushionability) Therefore, the adhesion of a film receiving material to the ink layer of a recording material is not good, resulting in formation of images having uneven image density. This is caused by uneven contact of the receiving material with the ink layer.
Paper receiving materials also have poor thermosensitivity. Although paper receiving materials have relatively good cushionability compared to the film receiving materials, the resultant images have uneven image density because the paper receiving materials have rough surface due to uneven distribution of paper fibers in the paper substrate.
In attempting to solve these problems, Japanese Patent Publication No. 6-84119 discloses a receiving material having a combination substrate in which a paper and a synthetic paper are adhered to each other. Japanese Patent Publication No. 8-32487 and Japanese Patent No. 2726040 (Japanese Laid-Open Patent Publication No. 63-87286) have disclosed paper receiving materials in which a receiving layer is formed on a paper substrate with an intermediate layer including foamed particles therebetween. It is described in the documents that the heat insulation property of the receiving materials is improved and therefore the image density of the resultant images is improved.
The receiving materials having a paper/synthetic paper substrate have good heat insulation property and good smoothness, however the materials have drawbacks in that they do not have a feeling of paper and have high manufacturing costs.
The receiving materials having an intermediate layer including foamed particles have good heat insulation property and cushionability, and therefore the thermosensitivity can be improved. However, the surface of the intermediate layer has rough surface because particles are dispersed in the layer. Since the intermediate layer has cushionability, the contact of the ink layer with the image receiving layer is improved to some extent when the recording material and the receiving material are pressed by a thermal head and a platen roller. However, the ink layer of the recording material unevenly contacts the receiving layer of the receiving material when microscopically observed. Therefore, the receiving materials are not suitable for current thermal transfer recording methods in which 128 or 256 levels of halftone images are produced. Japanese Laid-Open Patent Publication No. 9-99651 discloses a receiving material having an intermediate layer including hollow particles which have a weight average particle diameter of from 2 to 7 xcexcm and in which hollow particles having a particle diameter of from 2 to 6 xcexcm are present in an amount of not less than 50% by weight. It is described in the publication that by forming such an intermediate layer, the resultant receiving material has good cushionability, heat insulation property and surface smoothness, and therefore the receiving material has a feeling and a gloss like a paper as well as the receiving material can produce good images.
However, even when hollow particles having a particle diameter of from 2 to 6 xcexcm are present in an amount of not less than 50% by weight in the intermediate layer, the receiving material has a rough surface (i.e., projected portions due to the large particles and recessed portions due to broken large particles) when large particles are present in the layer. When images are formed on such rough portions, white spots tend to occur therein, resulting in deterioration of the images.
In addition, when a large particle is present in the layer, particles tend to adhere to the large particle, resulting in formation of aggregates of particles (i.e., formation of rough portions).
This white spot problem conspicuously occurs when images are formed by an n-fold speed mode multiple thermal recording method in which a receiving material is fed at a speed n (n greater than 1) times that of a recording material while their surfaces are rubbed together in the image forming process. The reason of occurrence of white spots in this process is considered to be that the hollow particles tend to be broken when the receiving material is rubbed with the recording material. This is confirmed by our examination in that when images are recorded with an edge type thermal head whose head pressure is larger than a partial-graze type plane thermal head, white spots (i.e., uneven images) caused by breaking of the hollow particles in the intermediate layer are produced more than in a case using the partial-graze type plane thermal head.
Japanese Laid-Open Patent Publication No. 10-129128 discloses a receiving material in which a thick receiving layer is formed on an intermediate layer having hollow particles such that the rough surface of the intermediate layer does not influence the surface smoothness of the receiving layer.
However, when such a thick receiving layer is formed, the cushionability and heat insulation property of the receiving material deteriorate, resulting in deterioration of image qualities and thermosensitivity. In addition, it takes a long time to prepare such a thick receiving layer because coating must be performed twice or more. Even when the thick layer is coated by one coating operation, it takes a long time to dry the coated liquid. Therefore, a problem which occurs is that manufacturing costs increase.
Because of these reasons, a need exists for thermal transfer receiving material on which images having good image qualities without uneven images can be formed with relatively low heat energy and which has relatively low manufacturing costs.
Accordingly, an object of the present invention is to provide a thermal transfer receiving material on which images having good image qualities can be formed with low heat energy and which has relatively low manufacturing; costs.
Another object of the present invention is to provide a thermal recording method in which images having good image qualities can be produced on the receiving material with relatively low heat energy at relatively low running costs.
To achieve such objects, the present invention contemplates the provision of a thermal transfer receiving material which includes a substrate, an intermediate layer which includes hollow particles and a binder resin and which is formed overlying the substrate, and a receiving layer which is formed overlying the intermediate layer, wherein each of the hollow particles in the intermediate layer has a particle diameter not greater than about 35 xcexcm. Each of the hollow particles preferably has a particle diameter not greater than about 30 xcexcm.
The surface of the intermediate layer preferably has a ten-point mean roughness Rz less than 4.0 xcexcm. The ten-point mean roughness is measured by a method based on JIS B0601.
In addition, preferably, the average hollow rate of the hollow particles is not less than 50%, and the thickness of the intermediate layer and receiving layer is from 10 to 100 xcexcm and not greater than 10 xcexcm, respectively.
In another aspect of the present invention, an n-fold speed mode thermal transfer recording method is provided which includes steps of feeding the receiving material mentioned above, and a thermal transfer recording material having an ink layer on one side thereof; and imagewise heating the recording material from the backside thereof to form an image on the receiving material while the ink layer contacts the receiving material, wherein the receiving material is fed at a speed n (n greater than 1) times the feeding speed of the recording material.
Preferably, the imagewise heating is performed using an edge-type thermal head and a recording material having plural color ink layers to form a color image on the receiving material.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction of with the accompanying drawings.